16' 3.5 ecoboost. Seems to run great but when the engine is cold you can feel a tiny misfire. It seems to be longer than a full revolution. Maybe after every 3 seconds at idle. Very minor but you can feel it. It use to go away after it warms up but now even at a light or in park you can still feel it later on.

plugs are new (did it before and after) and gapped well. No lights at all. Seems odd how it's consistent but does not occur enough to say it's every rotation....

 

Without knowing the full history I'd say it doesn't sound like anything to lose any sleep over.

Maybe run a couple of tanks of Premium and see if it runs idles any better? Italian tune up? Clean the Throttle body?